Experimental Determination of A Mid-Gap State Induced by Sulfur Vacancies on a MoS₂ Single Crystal
M. D. Siao1, W. C. Shen2, R. S. Chen1, Z. W. Chang3, M. C. Shih4, Y. P. Chiu3,4, Cheng-Maw Cheng5,6*
1Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan
2Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
3Department of Physics, National Taiwan Normal University, Taipei, Taiwan
4Department of Physics, National Taiwan University, Taipei, Taiwan
5Department of Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
6National Synchrotron Radiation Research Center, Hsinchu City, Taiwan
* Presenter:Cheng-Maw Cheng, email:makalu@nsrrc.org.tw
Two dimensional materials have demonstrated attractive properties for physical and technological applications since the discovery of graphene., The discovery of electronic structure transition from indirect to direct band gap in transition metal dichalcogenide (TMD) materials, such as MoS₂ monolayers, have opened up a new direction for photonic and optoelectronic applications involving TMD layer materials. These quasi-2D semiconductors are ideal systems to integrate with graphene for the development of next generation, ultrathin, flexible, transparent light emitting, light-harvesting and light-detecting devices.
Here we derive the electronic structure of MoS₂ single crystal. With angle-resolved photoemission spectroscopy (ARPES) measurement, we confirm that a major n-doping behavior on the surface of MoS₂ caused by the presence of surface electron accumulation (SEA) originates from a desulphurization process. These surface defects created by sulfur vacancies play a key role in the major physical origin of the SEA phenomenon. Our work provides an unprecedented insight into TMD layer materials, which have important implications in material processing, device design, and fundamental research.

Keywords: transition metal dichalcogenide, angle-resolved photoemission spectroscopy, electronic structure